Summary: Physical Aspects

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• 1 Basic physical concepts in food matrices

• 1.1 Solid states in food systems

• Which 2 physical states are there in solid systems?

  • Crystalline
    
  • Amorphous

• What is the difference the between crystalline and amorphous state?

  • Crystalline material --> atomic order at large scale
    
  • Amorphous --> no specific ordering of the atoms in the material

• How are crystalline and amorphous materials made?

  • Slow cooling --> atoms in material have time to order themselves --> crystalline state is formed
    
  • Faster cooling --> molecules slow down fast enough to prevent ordering of the molecules --> amorphous state

• What happens when you heat up a crystalline material?

  The ordered state will fall apart due to more molecular movement and the solid turns into a liquid at the melting temperature.

• What happens when you heat up an amorphous material?

  • The disordered arrangement of the solid material can rearrange. 
  • Above the glass temperature, the ability for rearrangement is high enough for it to move, and the material is called a rubber. 
    
  • Even higher T (melting temperature) --> convert into a crystalline state, where the molecules have an ordered arrangement

• 1.1.1 Interactions of water with solids

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• In which 2 ways can water interact with solids?

  • Adsorption on the surface of a solid (often a crystalline structure)
    
  • Adsorption within a solid (often amorphous) 

• What does the sorption of water by crystalline and amorphous structures (sugars, polymers and proteins) depend on?

  • Affinity of the material for water
    
  • The relative humidity 
  • Physical state of the solid

• Where does the sorption of water occur in crystalline solids?

  At the crystal surface. As the solid is already in an ordered arrangement, there is not space for the water to diffuse into. As the water cannot go into the solid, the sorption of water for crystalline solids is limited.

• When can the sorption capacity of crystalline solids be larger?

  When the solid has some impurities (some holes in the structure), the water might be able to fill this open spot in the arrangement.

• How does sorption of water in amorphous solids (amorphous sugar, proteins and polymers) occur?

  It has a less well-defined ordering. This will allow the water to diffuse into the material and fill the spaces in between the disordered molecules. These spaces, or 'sites' will fill up with water, and sorption within the material occurs.